The climactic battle in Dragon Ball Daima's finale pits Gomah against Goku, showcasing Goku's newly acquired form. Many anticipated this episode would finally explain Super Saiyan 4's absence from Super. So, how does the finale address this?
Episode 19 sees the Z Fighters revert to their adult forms after Glorio's wish. Vegeta's attempt to defeat Gomah, even as a Super Saiyan 3, fails. Goku then unleashes the power Neva granted him, revealing it as "Super Saiyan 4."
In this form, Goku battles Gomah, holding his own. A powerful Kamehameha blasts a hole through Gomah and the Demon Realm, allowing Piccolo to strike. While Piccolo doesn't deliver the final blow, Majin Kuu does, defeating Gomah and freeing the Demon Realm.
Instead of explaining Super Saiyan 4 as Demon Realm-exclusive or Neva-specific, Goku reveals he achieved the form through post-Buu training. The lack of a mind-wipe leaves Daima's canon status ambiguous.
Super Saiyan 4's introduction raises significant questions about Daima's place in the Dragon Ball canon. Its absence during Goku's fight with Beerus in Super, especially with Earth's fate at stake, is puzzling. While forgetting is possible, Vegeta's reaction to being surpassed again is unlikely.
However, a post-credits scene reveals two more Evil Third Eyes in the Demon Realm. A potential second season, involving these objects falling into the wrong hands, could offer a way to retcon Super Saiyan 4's introduction and its subsequent disappearance. This remains speculation, but its absence otherwise creates a significant plot hole.
This, then, is Dragon Ball Daima's explanation for Goku's lack of Super Saiyan 4 in Super. For those curious, here's a link to the anime's intro song.
Dragon Ball Daima is currently streaming on Crunchyroll.